1. Field of the Invention
The present invention relates to a lens device, and more particularly, to a click mechanism of a ring member of a lens device.
2. Description of the Related Art
JP-A-2007-219023 discloses a lens device used in a portable ENG (Electronic News Gathering) camera for television news. The lens device has a first MF mode that outputs an absolute position signal corresponding to the rotational position of a focus ring as an instruction to move the focus lens and a second MF mode that outputs a relative position signal corresponding to the amount of rotation of the focus ring as an instruction to move the focus lens, during a manual focus (MF) operation that manually operates the focus ring to move the focus lens, thereby adjusting focus.
FIG. 7 is an enlarged cross-sectional view illustrating a main part of the lens device disclosed in JP-A-2007-219023.
In the lens device, a first focus ring 4 and a second focus ring 5 are provided around a lens barrel body including, for example, a front frame 2 and a fixed ring 3. The first focus ring 4 is provided so as to be rotatable with respect to the lens barrel body and slidable in the optical axis direction. The second focus ring 5 is provided so as to be rotatable with respect to the lens barrel body only in a predetermined rotation range.
Gears 4A and 5A, which are clutch portions, are provided in portions of the first focus ring 4 and the second focus ring 5 facing each other. When the first focus ring 4 slides in the right direction of FIG. 7, the gear 4A is engaged with the gear 5A and the first focus ring 4 is connected to the second focus ring 5. In the state shown in FIG. 7, the gear 4A is disengaged from the gear 5A and the first focus ring 4 and the second focus ring 5 are not connected to each other.
During MF, when the first focus ring 4 and the second focus ring 5 are connected to each other, the operation mode is the first MF mode that outputs the absolute position signal corresponding to the rotational position of the second focus ring 5 as an instruction to move the focus lens. On the other hand, when the first focus ring 4 is not connected to the second focus ring 5, the operation mode is the second MF mode that outputs the relative position signal corresponding to the amount of rotation of the first focus ring 4 as an instruction to move the focus lens.
A cantilever-shaped cutout 4B for clicking is provided at the end of the first focus ring 4 opposite to the gear 4A, and a convex portion 2A that is fitted to the cutout 4B is provided on the front frame 2 facing the cutout 4B.
The cutout 4B for clicking formed in the first focus ring 4 and the convex portion 2A formed on the front frame 2 form a click mechanism. When the first focus ring 4 is moved to a first slide position where the first focus ring 4 is connected to the second focus ring 5 or a second slide position (state shown in FIG. 7) where the first focus ring 4 is not connected to the second focus ring 5, the click operation of the first focus ring 4 is performed by the click mechanism.
In the click mechanism of the lens device according to the related art, the cutout 4B for clicking is formed integrally with the first focus ring 4. Therefore, it is possible to reduce the number of parts. However, the click mechanism has the following problems.
The click mechanism has a problem in that it is difficult to obtain an initial click feeling with the use of the first focus ring 4. The reason is that the first focus ring 4 has the same linear expansion coefficient as the lens barrel body (for example, the front frame 2 and the fixed ring 3) made of an aluminum alloy and is generally made of, for example, polycarbonate in order to ensure strength and the cutout 4B for clicking which is made of, for example, polycarbonate gradually abrades with an increase in the number of click operations.
Six cutouts 4B for clicking are formed in the circumference of the first focus ring 4. During the slide operation of the first focus ring 4, the cutouts 4B only on one side (some cutouts) abrade due to the inclination of the first focus ring 4. It is considered that the inclination of the first focus ring 4 is caused because the cutout 4B for clicking is provided at the end of the first focus ring 4 and the contact width of the first focus ring 4 with the lens barrel body (the front frame 2 and the fixed ring 3) is small or because the first focus ring 4 slides on the front frame 2 and the fixed ring 3 and there is a step difference between the sliding surfaces of the front frame 2 and the fixed ring 3.
The cutout 4B for clicking is formed integrally with the first focus ring 4. Therefore, in order to determine an optimal click force, it is necessary to manufacture first focus ring samples including the cutouts 4B with different thicknesses, which results in an increase in manufacturing costs.